The first effective extractant capable of the selective recovery of rhodium3+ from hydrochloric acid solution, N-n-hexyl-bis(N-methyl-N-n-octylethylamide)amine (HBMOEAA), has been developed.
The extraction properties of palladium(II) in an HCl solution with four sulfide-containing monoamide (S-MA) compounds (N-methyl-N-n-octyl-4-thiapentanamide (MO4), N-methyl-N-n-octyl-3-thiapentanamide (MO3), N-methyl-N-noctyl-phenyl-3-thiapentanamide (MOPh), and N,N-di-n-octyl-3-thiapentanamide (DO3)) were investigated by solvent extraction, FT-IR, and EXAFS spectroscopies. All the S-MA compounds extract Pd(II) much faster than the conventional extractant, di-n-hexyl sulfide. The order of the extractabilities for Pd(II) is as follows: MO4 > DO3 ≈ MO3 > MOPh. The dominant extracted complex can be [PdCl 2 (S-MA) 2 ] for each S-MA system. The structural studies suggest that the inner coordination sphere of Pd(II) in the extracted complexes consists of 2 chloride ions and 2 sulfur atoms from a pair of S-MA molecules for all the systems. This means that the amide oxygen atom does not take part in the direct coordination to Pd(II), although the amide group can promote the Pd(II) extraction rate.
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